Method and apparatus for determining the acceptability of a weld formed by applying repetitive pulses of energy to the weld site

Abstract

Stress wave emission signals emanating from a weld during an AC welding operation are detected during (1) the time when the AC power is on, (2) the post weld time period, and (3) during each half-cycle of the AC weld when the absolute magnitude of the current is decaying. The stress wave emission signals are counted in each of these periods and compared to predetermined ranges of values to determine the acceptability of the weld.

What is claimed is: 
     
       1. A method of non-destructively determining, in real time, the acceptability of a weld formed by repetitive pulses of energy, wherein stress wave emission signals emanating from the weld site are monitored, the method comprising the steps of: counting and storing the number of excursions of the stress wave emission signals above a predetermined threshold during: (a) a first time period during the application of all the repetitive pulses of energy;   (b) a second time period after the termination of the last of the repetitive pulses; and   (c) a third time period comprised of the sum of all of the time intervals during which the absolute magnitude of each of the repetitive pulses is decaying;     comparing the stored counts with predetermined values to provide an indication of the acceptability of the weld in each of the time periods; and   combining the indication of acceptability from all of the comparing means to determine the acceptability of the weld.   
     
     
       2. The method as set forth in claim 1 wherein the count made in each of the time intervals is representative of the stress wave energy emitted from the weld site during the respective time intervals. 
     
     
       3. The method as set forth in claim 1 wherein the repetitive pulses of energy are provided by an AC welder. 
     
     
       4. The method as set forth in claim 1 wherein the repetitive pulses of energy are provided by a pulsed laser. 
     
     
       5. The method as set forth in claim 1 wherein the stored count of the first time period is compared to a predetermined value above which is indicative of an acceptable weld and at or below which indicates an unacceptable weld. 
     
     
       6. The method as set forth in claim 1 wherein the stored count of the second time period is compared to a predetermined value above which is indicative of an unacceptable weld and at or below which indicates an acceptable weld. 
     
     
       7. The method as set forth in claim 1 wherein the stored count of the third time period is comared to a predetermined value above which is indicative of an unacceptable weld and at or below which indicates an acceptable weld. 
     
     
       8. The method as set forth in claim 1 wherein in the combining step all the indications determined by the comparing step must be acceptable for the weld to be considered acceptable. 
     
     
       9. An apparatus for non-destructively determining, in real time, the acceptability of a weld formed by repetitive pulses of energy, wherein stress wave emission signals emanating from the weld site are monitored, the apparatus being comprised of the combination of: means for counting and storing the number of excursions of the stress wave emission signals above a predetermined threshold during: (a) a first time period during the application of all the repetitive pulses of energy;   (b) a second time period after the termination of the last of the repetitive pulses; and   (c) a third time period comprised of the sum of all of the time intervals during which the absolute magnitude of each of the repetitive pulses is decaying;     means for comparing the stored counts with predetermined values to provide an indication of the acceptability of the weld in each of the time periods; and   means for combining the indication of acceptability from all of the comparing means to determine the acceptability of the weld.   
     
     
       10. An apparatus as set forth in claim 9 wherein the count made in each of the time intervals is representative of the stress wave energy emitted from the weld site during the respective time intervals. 
     
     
       11. The apparatus as set forth in claim 9 wherein the repetitive pulses of energy are provided by an AC welder. 
     
     
       12. The apparatus as set forth in claim 9 wherein the repetitive pulses of energy are provided by a pulsed laser. 
     
     
       13. The apparatus as set forth in claim 9 wherein the stored count of the first time period is compared to a predetermined value above which is indicative of an acceptable weld and at or below which indicates an unacceptable weld. 
     
     
       14. The apparatus as set forth in claim 9 wherein the stored count of the second time period is compared to a predetermined value above which is indicative of an unacceptable weld and at or below which indicates an acceptable weld. 
     
     
       15. The apparatus as set forth in claim 9 wherein the stored count of the third time period is compared to a predetermined value above which is indicative of an unacceptable weld and at or below which indicates an acceptable weld. 
     
     
       16. The apparatus as set forth in claim 9 wherein the indications received by the combining means from all of the comparing means must be acceptable for the weld to be considered acceptable. 
     
     
       17. An apparatus for non-destructively determining, in real time, the acceptability of an AC weld wherein stress wave emission signals emanating from the weld site are monitored, the apparatus being comprised of the combination of: a sensor mounted proximate the weld site to sense the stress wave emission signals emanating from the weld;   an amplifier, to amplify the stress wave emission signal output from the sensor;   a first, a second and a third stress wave emission signal analyzer connected electrically in a parallel relationship to simultaneously receive the stress wave emission signals from the amplifier;   each of the stress wave emission signal analyzers being comprised of: a threshold detector to detect each excursion of the stress wave emission signals that are above a preset threshold;   a counter to count and accumulate pulses from the threshold detector, each pulse being representative of an excursion of the stress wave emission signal passing above the threshold; and   a comparator to compare the accumulated count from the counter with a predetermined count to provide an indication of the acceptability of the weld;     the first signal analyzer accumulates a count during a first time window encompassing the application of all of the AC pulses;   the second signal analyzer accumulates a count during a second time period after the termination of the last of the AC pulses;   the third signal analyzer accumulates a count during a third time period comprised of the sum of all of the time intervals during which the absolute magnitude of each of the AC pulses is decaying; and   a utilization circuit for combining the indication of acceptability from all of the time intervals to determine the acceptability of the weld.